One of the primary reasons for interest in offering IP/internet telephony services is the pricing structures currently in place for the data services, and voice services offered by telephone operators. Long distance voice service can be thought of as “demand data” service, where the user pays a premium for the instantaneous access to a 64 Kbps channel (voice grade channel in the U.S.). Widely publicized, promotional type pricing for this service Is on the order of $0.10 a minute. By contrast, data service offered by telephone operators, such as that offered for a T-1 connection (24 voice quality data lines, for a 1.544 Mbps connection) is priced at approximately $1000/month, which works out to $0.001 a minute per voice line. In the very near future, cable operators will place extreme pressure on even the data service rates for telephone operators, as cable modems will allow cable operators to offer hundreds of Kbps effective throughput for approximately $50/month.
IP telephony is also one of the first and most visible steps toward an Integrated Services Internet, which carries real time data, voice and video.
The basic Idea of IP/internet voice telephony is to digitize your voice as you talk on the phone and send the digitized data as IP packets to the Internet. An IP voice device can be embedded within an Internet connection device such as a modem, a set-top-box, or a computer. It can be also built as a stand alone product. The stand alone IP voice device, for example, may provide an Ethernet jack which can be connected with an Internet connection device and other LAN devices. The IP voice device may also include interfaces to connect regular phone handsets. The quality of speech heard through a normal telephone line requires 64 kbits/s bandwidth. However, most current internet connections have less bandwidth, such as 28.8 kBPS, or 56 kBPS modem. Furthermore, even if a fast connection device is used, such as an ISDN, or Cable Modem, the Internet network itself is a shared medium and has limited bandwidth. Therefore, audio codecs are usually embedded to compress the voice data.
To guarantee the interoperability between IP voice devices from different vendors, International Telecommunications Union (ITU) developed H.323 as the standard for telephony over IP network. H.323 defines common procedures for call setup, data compression, and data transport.
H.323 is an umbrella standard which references many other ITU recommendations. It provides various levels of multimedia communications. These levels include voice only, voice and video, voice and data, or voice, video, and data communications over a local area network. The voice only H.323 protocol stack includes RTP/RTCP, RAS/Q.931 (H.225,0), and H.245. RTP/RTCP is used for packetization and synchronization of voice data. RAS/Q.931 describes the call registration, admission, and status as well as call signaling. H.245 defines the control messages and procedures.
In a general sense, IP telephony can be thought of has providing a “virtual” point to point connection for voice services over Internet. Various IP telephony devices currently exist in the marketplace. Some examples include VocalTec® Internet Phone® Lite which is a software product to be used in a multimedia PC, made by Vocaltech Corporation of Northvale, N.J. Other examples of product include CoolTalk of Netscape or NetMeeting of Microsoft. Most of these software based products reside in a client server such as a PC or a network computer (NC) that require a microphone, speaker and a sound card. Other products come in the form of a handset, which basically incorporates the function of the microphone and speaker in the software-based product.
As an example of how to place a call, suppose a user in Indianapolis wants to call his friend in Paris. He would pick up his IP voice device handset (or a virtual handset on the computer screen) and hear a dial-tone like a regular telephone dial-tone. Then, he dials his friend's Paris phone number. The call travels over the Internet to a server provided by the IP telephony service provider. The server connects the call to his friend's IP voice device and initiates the call. If his friend has only a regular telephone, the server will connect the call to a gateway in Paris. The gateway in Paris then initiates a call over the public switched telephone network (PSTN) to the local Paris number.
Depending on the Internet connections, there are basically two methods for making calls using an IP voice device: dial-up connections, and direct connections.
With a dial-up connection, a user first calls an ISP (Internet service provider) over a regular dial-up line to set up an Internet connection. Then, he will use the IP voice device handset to dial the phone number of the person he is calling. With a direct or permanent connection, a user places a call using the IP voice device just as he does with the regular telephone. The direct connection indicates a permanent open channel to the Internet such as ISDN, or a cable access device. For dial-up connection call, a phone that has been called won't ring unless the Internet connection is already established for this phone. For direct connection call, a phone would ring like a normal telephone.
European Patent Application, EP-A-0781016, discloses a known Internet telephone system. The system disclosed allows a server connected to a called device to use the telephone number of the telephone line connected to the called device, in order to set up the internet telephone call. However, there still needs to be an efficient and easily implementable way to further distinguish whether a call to the called device is an internet call or a regular telephone call, so that the call may be handled correctly and automatically.